External extractor fan for exhaust hood

ABSTRACT

An external fan for an extractor device, wherein the external fan includes a fan housing; a ventilator housing that is arranged in the fan housing and that has an air discharge; and a sound absorbing member that is arranged in the fan housing and that is opposite the air discharge of the ventilator housing.

BACKGROUND OF THE INVENTION

The invention relates to an external fan for an extractor device, in particular to an external fan for an extractor hood.

In extractor hoods a fan, via which fumes and vapors are sucked up into the extractor hood, is generally provided in a fan housing that is located directly above or behind the intake opening. In this instance the intake opening is covered by a fat filter. However, there are also extractor hoods in which only a housing with an intake opening is provided in the room where the fumes and vapors are produced, in particular the kitchen, whilst the fan, via which the vacuum required to suck up fumes and vapors is produced, is fixed to the outer face of the room wall, in particular to the house wall. These fans are also known as external fans and are connected to the housing in the room via pipework or ducts.

Specific demands are placed on these external fans. In particular, the volume flow conveyed by the fan must be greater than with a fan that is arranged directly in the vicinity of the intake opening in order to ensure reliable suction of fumes and vapors. A drawback of this required volume flow is that more noise is also produced. In addition, with external fans the regions at which air can be blown out from the fan are defined since the infiltration of moisture and impurities from the surrounding environment into the housing must be avoided.

DE 86 01 684 U1 describes a cooling fan for an electric machine. With this fan a sound-absorbing layer is attached to the spiral housing of a radial ventilator, in which layer the blow-out opening in the spiral housing is reproduced. The air outlet from the spiral housing is therefore not disturbed. A drawback of this fan is that the air flow from the blow-out opening in the spiral housing to the air outlet from the fan also produces noise.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to make it possible to operate an external fan with sufficient volume flow and wherein the noise produced during operation of the external fan can simultaneously be reduced.

The invention is based on the knowledge that this object can be achieved by providing a sound-absorbing member in the vicinity of the air outlet in the ventilator housing in the direction of flow of the air exiting the ventilator housing. This means that a sound absorber is arranged downstream of a fan component, in which the ventilator is provided.

The object is therefore achieved by an external fan for an extractor device, said fan comprising a fan housing and a ventilator housing received in the fan housing. The external fan is characterized in that at least one sound-absorbing member is provided in the fan housing opposite the air discharge in the ventilator housing.

Within the meaning of the present invention an external fan denotes a fan that is fixed to an outer wall of a building or to the roof of a building and is connected to at least one extractor device in a room of the building via pipework or a duct. In this instance the extractor device in the room preferably does not comprise a fan, but does have an intake opening, via which the air to be cleaned can enter the extractor device. The fan housing of the external fan constitutes the outer housing, which is in direct contact with the surrounding environment, i.e. the outside environment. The fan housing is generally box-shaped, wherein an air inlet opening is provided in a side wall and air outlet openings are provided in the lower face and/or in regions of the side walls. In this instance the lower face means the face pointing downward when the fan is assembled fixed to a vertical wall.

The ventilator of the fan according to the invention is preferably a radial ventilator. In this instance pressure is accelerated owing to the centrifugal force of the rotating ventilator component, this acceleration being further intensified by the ventilator housing surrounding the ventilator. It is possible to achieve volume flows of up to more than 1000 m³/h using a radial ventilator. The ventilator housing is preferably a spiral housing having an air intake opening on one or both sides and an air discharge somewhere at the periphery. In particular the air discharge is formed by a pipe socket. The pipe socket may be configured as part of the ventilator housing or as a separate part and may be attached to the opening of the ventilator housing.

In accordance with the present invention the sound-absorbing member is arranged in such a way that it is opposite the air discharge in the ventilator housing. According to the present invention this means that the sound-absorbing member covers the air discharge, at least in part, as it projects toward the air discharge against the direction of the air flow. However, in this instance the sound-absorbing member is arranged in such a way that there is a distance, at least in part, between the surface of the air discharge and the sound-absorbing member. The entire sound-absorbing member is preferably arranged at a distance from the air discharge.

Owing to the arrangement of a sound-absorbing member opposite the air discharge in the ventilator housing it can be ensured that the majority of the air exiting the ventilator housing flows over the sound-absorbing member. The noise emitted by the ventilator is therefore intercepted in the sound-absorbing member arranged opposite the air discharge. The air discharge noise from the fan housing can thus be reduced by the sound-absorbing member. In a preferred embodiment the sound-absorbing member completely covers the air discharge in the ventilator housing by projecting toward this air discharge. It is therefore ensured that the entire air flow from the ventilator housing flows over the sound-absorbing member.

The sound-absorbing member is preferably arranged at a housing wall of the fan housing, said housing wall being arranged opposite the air discharge in the ventilator housing. Air outlet openings for the air outlet from the fan housing may be provided in this housing wall of the fan housing. However, the housing wall may also be a closed wall. The housing wall at which the sound-absorbing member is provided is preferably arranged parallel to the surface of the air discharge in the ventilator housing and therefore generally perpendicular to the direction of flow of the air exiting the ventilator housing.

In the simplest case the sound-absorbing member is a sound-absorbing panel or a sound-absorbing mat. In this case the efficacy of the sound absorption is affected by the thickness of the sound-absorbing mat since the spectrum of noise intercepted by said mat depends on the thickness of the absorbing layer. For example, with a small thickness noise in the upper frequency range is primarily intercepted.

In accordance with a further embodiment the sound-absorbing member varies in thickness over the surface thereof In particular the sound-absorbing member may, for example, be shaped like a cone, a truncated cone, a wedge, a pyramid or a roof In this instance one face of the sound-absorbing member is preferably planar. The sound-absorbing member can be applied and fixed to the housing wall of the fan housing via this face. The planar face of the sound-absorbing member thus faces away from the air discharge when assembled.

A wide frequency spectrum can be intercepted since the sound-absorbing member varies in thickness. In addition a sound-absorbing member may also fulfill an air-guiding function owing to the three-dimensional geometry of the sound-absorbing member. In particular the air exiting the air discharge may be guided selectively toward air outlet openings in the fan housing. The flow resistance is therefore reduced compared to a sound-absorbing panel or a sound-absorbing mat as a result of the selective air guidance at the sound-absorbing member owing to its geometry. The sound power of the external fan can therefore be reduced by a sound-absorbing member varying in thickness.

In accordance with a preferred embodiment the sound-absorbing member, which varies in thickness over its surface, is thickest at a point corresponding to the centre of the air discharge in the ventilator housing. With a rotationally symmetrical sound-absorbing member and a circular air discharge the sound-absorbing member and the air discharge are arranged concentrically to one another. The point corresponding to the centre of the air discharge is the point of the sound-absorbing member arranged in the centre of the air discharge when said sound-absorbing member is assembled projecting in a perpendicular manner toward this point and toward the air discharge. The air exiting the air discharge is split and therefore distributed owing to this configuration of the sound-absorbing member. Following the splitting process the air flows over and along the thinner regions of the sound-absorbing member and can therefore reach air outlet openings in the fan housing. The surface of the air outlet from the fan housing is therefore increased, thus decreasing the exit velocity. As well as absorbing noise, the sound-absorbing member therefore also reduces noise production.

If the sound-absorbing member is shaped such that the greatest thickness of the sound-absorbing member extends over the width or length of the sound-absorbing member, then the sound-absorbing member is preferably arranged in such a way that the line of the highest elevation passes through the point corresponding to the centre of the air discharge in the ventilator housing. With this configuration the sound-absorbing member may, for example, be wedge-shaped or roof-shaped. The air flow exiting the air discharge in the ventilator housing is split into two partial flows at a sound-absorbing member of this type, once the air flow has contacted the sound-absorbing member. The different frequencies are therefore intercepted by the sound-absorbing member and air is also guided selectively.

In accordance with a further embodiment at least one lateral sound-absorbing part is provided in the fan housing and forms a sound-absorbing body together with the sound-absorbing member. In this instance the lateral sound-absorbing part is therefore arranged in such a way that it lies outside the surface of the air discharge and projects in a perpendicular manner toward the air discharge. On the one hand additional regions for noise absorption are formed by providing lateral sound-absorbing parts in the fan housing. On the other hand the air guidance function is improved since the air is now guided at the sound-absorbing member and at the one or more lateral sound-absorbing parts, in particular between the sound-absorbing member and the lateral sound-absorbing part. In this instance the shape of the lateral sound-absorbing part or lateral sound-absorbing parts is selected as a function of the shape of the sound-absorbing member. In particular one or more channels are formed between the sound-absorbing member and the lateral sound-absorbing parts. These channels are preferably designed in such a way that the channel cross-section increases from the upper face of the sound-absorbing body toward the lower face thereof or toward the lateral sides thereof. The exhaust velocity of the air from the outlet openings in the fan housing is thus reduced and noise production is therefore further minimized.

In accordance with a further embodiment the sound-absorbing member completely covers the housing face of the fan housing, the housing face being arranged opposite the air discharge in the ventilator housing. In this case the surface that is available for noise absorption may be maximized and air can also be guided continuously from the air discharge to the sides of the device housing. The noise emitted by the ventilator discharge or ventilator socket is therefore better intercepted. Alternatively however, the sound-absorbing member may also cover only part, in particular the central part of the housing face of the fan housing, said housing face being arranged opposite the air discharge in the ventilator housing. In this case the edge region at the sound-absorbing member is available for air outlet openings from the fan housing.

The fan housing may comprise air outlet openings in the housing face opposite the air discharge in the ventilator housing and/or in housing faces adjacent thereto. The air outlet openings in the housing face that is arranged opposite the air discharge, and in particular constitutes the lower face of the fan housing, may be provided distributed over the entire surface of this housing face. For example a perforated plate may be used as the lower face of the fan housing. In this embodiment the sound-absorbing member is applied to the perforated plate and optionally fixed thereto. However it is also possible to provide merely the edge region of the lower face with air outlet openings. In this case the central region, in which there are no air outlet openings, is selected in such a way that it corresponds to the shape of the sound-absorbing member that will be placed on the perforated plate. Air outlet openings may also be provided in the faces of the fan housing that are adjacent to the lower face, in particular the side walls and the front face of the fan housing. At these housing faces or housing walls the air outlet openings are only provided in the lower region, i.e. in the vicinity of the base of the fan housing. The openings in the side walls and in the front face may also be formed by round holes. However, it is also possible to select other types and shape of opening. For example, these openings may be formed by slots or by a single opening covering the entire region that is defined for the air outlet. The air outlet openings are provided in the side walls and/or in the front face, in particular in the embodiments in which the sound-absorbing member covers the entire housing face arranged opposite the air discharge.

In accordance with a further embodiment the sound-absorbing member comprises a partition wall that extends perpendicular to an elevation in the sound-absorbing member. In this embodiment the features of optimized air guidance, interception of a wide frequency spectrum owing to the varying thicknesses of the sound-absorbing member caused by the elevation, and the use of a partition wall are combined. As a result of the partition wall the sound-absorbing member acts as a splitter silencer. In addition the provision of a partition wall leads to greater stability of the sound-absorbing member. In particular a wall that extends upwardly and in a perpendicular manner from a planar lower face of the sound-absorbing member is denoted as the partition wall. In this instance the height of the partition wall may correspond to the height of the elevation of the sound-absorbing member. A point or line that is taller than the wider regions of the sound-absorbing member denotes an elevation. This type of sound-absorbing member is advantageously used, in particular, in a fan housing in which the air outlet openings are provided in the side walls of the fan housing. In this instance the partition wall extends perpendicular to the side walls of the fan housing.

In accordance with one embodiment the sound-absorbing member consists of two shells. In particular this construction is advantageous for a sound-absorbing member comprising a partition wall. More specifically, in this case two shells configured as channel halves may be arranged side by side and the adjacent channel sides projecting upwardly form the partition wall. In addition a metal plate may be placed between the shells or channel halves. This further increases the stability of the sound-absorbing member. In this embodiment geometries of the shells are preferably such that the thickness of the sound-absorbing member varies over the length of the shell.

In accordance with some embodiments the sound-absorbing member is symmetrical in shape. In particular a mirror-symmetrical shape and a rotationally symmetrical shape are preferred. In addition to uniform noise absorption and selective air guidance, the symmetry simplifies production of the sound-absorbing member.

The sound-absorbing member is preferably provided in the vicinity of the air discharge in the ventilator housing. In accordance with one embodiment the distance between the highest point of the sound-absorbing member and the air discharge is at most one third, preferably at most one quarter of the diameter of the air discharge. Owing to the short distance to the air discharge it is ensured that air exiting the air discharge arrives at the sound-absorbing member and this may provide noise reduction. In addition selective air guidance can be created by the sound-absorbing member merely owing to the short distance to the air discharge since the air flow exiting the air discharge is still directed. By contrast, with a sound-absorbing member arranged at a greater distance from the air discharge the air flow will already be undirected by turbulences, thus making selective air guidance by the sound-absorbing member difficult or impossible.

As already described above, the fan housing may consist of a box-shaped housing and may therefore be formed in one piece. In this case a dividing wall is generally provided inside the fan housing. This dividing wall divides the interior into an upper and a lower housing region. The inlet opening for the air inlet is provided in the upper housing region in the rear face. The ventilator housing is also received in the upper region. A passage is provided in the dividing wall, through which passage the air discharge in the ventilator housing may extend or to which the air discharge may be fitted. The size of the passage corresponds to the inner or outer dimensions of the air discharge, for example of a pipe socket. The sound-absorbing member, optionally with lateral sound-absorbing parts, is received in the lower region of the fan housing. In addition air outlet openings are provided or formed in the lower region of the housing in the lower face, front face and/or the side walls.

In accordance with an alternative embodiment the fan housing is in two parts and one part of the fan housing receives the sound-absorbing member and comprises the at least one air outlet opening in the fan housing. In this embodiment the sound-absorbing member or the sound-absorbing body thus forms a self-supporting member together with a sheet metal housing. This is fixed to the lower face of the upper part of the fan housing. The construction of the upper part of the fan housing and the components contained therein correspond to those of the upper housing region, which was described with reference to the one-piece fan housing. The sound-absorbing member with a sheet metal housing may be used as an accessory and may be used to retrofit existing installations. When retrofitting, merely the lower separate housing part is mounted from below to a fan housing that is already present.

In accordance with the invention it is also possible, however, to fix a sound-absorbing member to the protective grating of a fan housing that is already present, i.e. installed, and in particular to clamp it below the protective grating.

For example, in accordance with the invention foamed material is used as the material for the sound-absorbing member and optionally for the lateral sound-absorbing part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained again hereinafter with reference to the accompanying figures illustrating various embodiments of the fan housing according to the invention and in which:

FIG. 1: is a perspective rear view of a first embodiment of the fan according to the invention;

FIG. 2: is a schematic sectional view of the first embodiment according to FIG. 1;

FIG. 3: is a perspective rear view of a second embodiment of the fan according to the invention;

FIG. 4: is a schematic sectional view of the second embodiment according to FIG. 3;

FIG. 5: is a schematic sectional view of a third embodiment of the fan according to the invention;

FIG. 6: is a perspective rear view of a fourth embodiment of the fan according to the invention;

FIG. 7: is a schematic sectional view of the fourth embodiment according to FIG. 6;

FIG. 8: is a perspective rear view of a fifth embodiment of the fan according to the invention;

FIG. 9: is a schematic sectional view of the fifth embodiment according to FIG. 8;

FIG. 10: is a perspective view of an embodiment of a sound-absorbing member of the fan according to the invention;

FIG. 11: is a perspective rear view of a sixth embodiment of the fan according to the invention; and

FIG. 12: is a schematic sectional view of the sixth embodiment according to FIG. 11

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

FIGS. 1, 3, 6, 8 and 11 each illustrate a perspective rear view of embodiments of the fan 1 according to the invention. In all these embodiments the fan housing 10 comprises the same basic construction. The fan housing 10 is box-shaped. The upper face 101, which may also be denoted as the cover, is inclined in the embodiment shown. Furthermore, the fan housing 10 comprises a rear face or rear wall 102, two side walls 103 and a front face 105, which is not visible in the views shown. Lastly the fan housing 10 comprises a lower face 104, which is also denoted as the base.

An air inlet opening 1021 is provided in the rear face 102. A pipe may be connected to this air inlet opening 1021, which has a circular cross-section, via which pipe the external fan 1 can be connected to the extractor device (not shown), which is provided in a room in the building to which the external housing 1 is fixed. In the perspective views shown the lower region of the rear face 102 is not shown in order to make it possible to view inside the fan housing 10. However, with the fan housing 10 the rear wall 102 extends over the entire height of the fan housing 10, i.e. as far as the lower face 104 of the fan housing 10.

As can be seen from the respective sectional views 2, 4, 7, 9 and 12, the interior of the fan housing 10 is divided into an upper and a lower part 10 a, 10 b or portion. These are separated from one another by a dividing wall 11. The dividing wall 11 extends in a horizontal direction and covers the entire surface between the front face 105, the rear wall 102 and the side walls 103. A passage 111 is provided in the dividing wall 11.

The ventilator housing 2 of the ventilator (not visible) is arranged in the upper part 10 a of the fan housing 10. The intake openings 21 in the ventilator housing 2 are located in the sides of the ventilator housing 2. The lower end of the ventilator housing 2 is formed by the air discharge 22. This air discharge 22 is shaped like a pipe socket. The pipe socket extends through the passage 111 into the lower part 10 b of the fan housing 10.

In the first embodiment, shown in FIGS. 1 and 2, a sound-absorbing member 3 in the form of a sound-absorbing mat 31 is arranged in the lower part of the fan housing 10 on the lower face 104 or on the base of the fan housing 10. The sound-absorbing mat 31 is rectangular. The sound-absorbing mat 31 is arranged in such a way that it lies at a distance from the side walls 103 of the fan housing 10. The sound-absorbing mat 31 is also arranged at a distance from the front face 105 and the rear face 102 of the fan housing 10. The sound-absorbing mat 31 is oriented in such a way that it lies projecting in a perpendicular manner below the air discharge 22 in the ventilator housing 2. Air outlet openings (not shown) are formed in the lower face 104 of the fan housing 10, at least in the edge region that exists between the sound-absorbing mat 31 and the side walls 103 and between the front face 105 and the rear wall 102.

Air that enters the upper part 10 a of the fan housing 10 via the air inlet opening 1021 is transported to the interior of the ventilator housing 2 through the intake openings 21. The air exiting the ventilator housing 2 arrives in the lower part 10 b of the fan housing 10 via the air discharge 22. Since the sound-absorbing mat 31 is arranged opposite the air discharge 22, the air exiting the air discharge 22 arrives directly at the sound-absorbing mat 31 where noise of a specific frequency can be absorbed. The air is then released into the surrounding environment via the air outlet openings in the fan housing 10. The air guidance in this embodiment is indicated schematically in FIG. 1 by the arrows.

In accordance with a second embodiment, shown in FIGS. 3 and 4, the sound-absorbing member 3 is shaped like a straight circular cone 32. The circular base 321 of the circular cone 32 lies on the lower face 104 of the fan housing 10. In this instance the diameter of the circular cone 32 is dimensioned in such a way that it basically corresponds to the diameter of the air discharge 22 in the ventilator housing 2. The circular cone 32 is arranged projecting in a perpendicular manner beneath the air discharge 22 in the ventilator housing 2. The circular cone 32 is therefore arranged at a distance from the side walls 103, the front face 105 and the rear wall 102. Air outlet openings (not shown) are provided in the gap formed by this distance. In the embodiment shown the circular cone 32 is cylindrical in its lower region. The height of the circular cone 32 at its central point is dimensioned in such a way that there is a shorter vertical distance between this central point and the lower face of the air discharge 22 in the ventilator housing 2. In this embodiment the air exiting the air discharge 22 is fanned out owing to the conical shape of the sound-absorbing member 3 and is distributed over the periphery of the circular cone 32. The air is therefore guided selectively along the circular cone 32 toward the lower face 104 of the fan housing 10, where the air may exit via air outlet openings (not shown) into the surrounding environment. Since the circular cone 32 may vary in height over the base 321 thereof, it can absorb noise of varying frequency. The outlet surface via which air may exit the fan housing 10 is additionally increased owing to the air flow being fanned out and therefore the exit velocity is reduced. This leads to further noise reduction.

In the third embodiment, shown in FIG. 5, additional lateral sound-absorbing parts 33 are provided besides the sound-absorbing member 3 in the shape of a circular cone 32. These lateral sound-absorbing parts 33 are provided at the lower face of the dividing wall 11 along the front face 105, the rear wall 102 and the side walls 103. In this instance the lateral sound-absorbing parts 33 are wedge-shaped and are attached in such a way that the side facing the circular cone 32 is a slope. The air guidance is thus further improved and further surfaces are also created for noise absorption.

The second and third embodiments may also be modified in such a way that the sound-absorbing member 3 is wedge-shaped instead of being in the shape of a circular cone. In this case the base of the sound-absorbing member 3 is rectangular and the slopes of the wedge or roof extend downwardly from the centre of the sound-absorbing member 3 toward two sides in the direction of the lower face 104 of the fan housing 10. In this modified embodiment the lateral sound-absorbing parts 33 are only provided along the side walls 103 at the lower face of the dividing wall 11. In this modified embodiment the air flow from the air discharge 22 is split into two partial flows.

A fourth embodiment is shown in FIGS. 6 and 7. In this embodiment air outlet openings 1031 are provided in the side walls 103 of the fan housing 10 in the region of the lower part 10 b of the fan housing 10. In the embodiment shown the air outlet openings 1031 are formed by rectangular openings, which extend as far as the front edge and the rear edge of the side wall 103. However, it is also possible for the air outlet openings 1031 to be formed by perforations in the lower region of the side walls 103.

In accordance with the fourth embodiment the sound-absorbing member 3 is in the shape of a roof 34. In this instance the base 341 covers the entire lower face 104 of the fan housing 10. The upper face of the roof 34 is formed by two curved roof faces 342, which extend upwardly toward the centre of the roof 34. The roof apex 343 is rounded. The roof apex 343 lies in the centre of the sound-absorbing member 3 and projects in a perpendicular manner toward the air discharge 22 along the diameter of the air discharge 22. The roof 34 is tallest at the centre. At this point the roof apex 343 is arranged only at a short distance from the lower face of the air discharge 22. At the sides of the roof 34, which abut the side walls 103 of the fan housing 10, the height of the roof 34 is so low that it merely corresponds to the height of the lower edge, which is formed by the air outlet opening 1031 in the side wall 103. As a result of this construction the air flow exiting the air discharge 22 contacts the roof apex 343 and is split there. The air is guided along the curved roof faces 342 toward the air outlet openings 1031 in the side walls 103 and can exit there. In this embodiment the face arranged opposite the air discharge 22, i.e. the lower face 104 of the fan housing 10 is utilized entirely for sound-absorbing measures. Since the sound-absorbing member 3 also varies in thickness many times over its surface owing to the roof shape, a large number of various frequencies can also be absorbed by the sound-absorbing member 3.

The fifth embodiment, shown in FIGS. 8 and 9, basically corresponds to the fourth embodiment, in particular air outlet openings 1031 are also provided in the side walls 103 of the fan housing 10 in the fifth embodiment. In addition the sound-absorbing member 3 is also roof-shaped. However, in the fifth embodiment a partition wall 35 is provided. This partition wall 35 extends vertically toward the base 341 of the roof-shaped sound-absorbing member 3 and lies perpendicular to the direction of the roof apex 343. In the embodiment shown the partition wall 35 thus extends from a side wall 103 to the opposite side wall 103. The height of the partition wall 35 corresponds to the height of the sound-absorbing member 3 at the roof apex 343. Owing to the partition wall the sound-absorbing member 3 acts like a splitter silencer. The air flow exiting the air discharge 22 is divided into two partial flows, extending opposite one another, by the roof apex 343, these partial flows each being divided in turn into two further partial flows owing to the partition wall 35. The partition wall 35 thus also improves air guidance in addition to improving sound absorption. Lastly, the partition wall 35 affords the sound-absorbing member 3 greater stability, which, in particular, prevents deformation of the sound-absorbing member 3.

A further embodiment of a sound-absorbing member 3 is shown in FIG. 10, which sound-absorbing member can be used in a fan 1 according to the invention. In this embodiment the sound-absorbing member 3 consists of two shells 36. The shells 36 have a U-shaped cross-section. The base of each of the shells 36 is a planar surface, from which the side branches of the shells 36 point upwardly. Each of the shells 36 has a roof-shaped geometry corresponding to the roof shape described with reference to FIGS. 8 and 9. A metal plate 37 is provided between the abutting side branches of the two shells 36. This therefore forms a partition wall 35 together with the adjacent side branches of the shells 36. The sound-absorbing member 3 shown in FIG. 10 is used in a fan housing 10 comprising air outlet openings 1031 in the side walls, as shown in FIGS. 8 and 9. Owing to the construction in two parts it is possible to further increase the stability of the sound-absorbing member 3 using a metal sheet 37.

Lastly, FIGS. 11 and 12 show a sixth embodiment of the external fan 1 according to the invention. In this embodiment the sound-absorbing member 3 forms part of a sound-absorbing body 38. The sound-absorbing body 38 fills the entire lower part 10 b of the fan housing 10, i.e. the region between the dividing wall 11 and the lower face 104. In this instance the sound-absorbing member 3 is rotationally symmetrical in shape, in particular it is in the shape of a truncated cone. The diameter of the base 391 of the truncated cone 39 corresponds to the diameter of the air discharge 22 in the ventilator housing 2. In this embodiment the upper face of the truncated cone 39 lies at the height of the lower face of the air discharge 22 or even also projects into the ventilator housing 2. The truncated cone 39 is connected to the edge part 382 of the sound-absorbing body 38 via webs 381. An annular channel 383 is formed between the edge part 382 and the truncated cone 39, via which channel air may arrive from the air discharge 22 via the sound-absorbing body 38 to the lower face 104 of the fan housing 10. Air outlet openings (not shown) are provided in the lower face 104 and allow the air to exit the fan housing 10 and to be released into the surrounding environment. The annular channel 383 is configured in a diffuser-like manner. This means that the width of the channel at the upper face of the sound-absorbing body 38, at which upper face the sound-absorbing body abuts the air discharge 22, is smaller than at the lower face of the sound-absorbing body 38, at which lower face the sound-absorbing body abuts the lower face 104 of the fan housing 10.

As can be seen in FIG. 11, in this embodiment the channel 383 is selected to be of such a width that it ends at the front face 105 and the rear wall 102 of the fan housing 10. Curved openings in the sound-absorbing body 38 thus exist at the front face 105 and the rear wall 102. In addition to the air outlet it is thus possible to deliver air into the surrounding environment via the lower face 104 by a corresponding air outlet opening in the front face 105.

The invention is not limited to the embodiments shown. In particular individual features of one embodiment may be applied in another embodiment without also having to apply all the other features of the described embodiment to the other embodiment.

In the new concept of the external fan a sound absorber with a sound-absorbing member is integrated inside the housing and is connected to the air outlet socket of the ventilator or is arranged downstream thereof. It is compulsory for the exiting air to escape from the ventilator via the sound absorber, the air outlet noise thus being reduced by the sound absorber used. The sound-absorbing means is configured in such a way that the noise emitted by the fan is intercepted in a sound-absorbing medium arranged opposite the outlet region.

A range of advantages can be obtained with the present invention. In particular the advantages lie in noise reduction. The sound power level is thus reduced by the downstream sound absorber, which comprises the sound-absorbing member. In addition the flow velocity of the air can be selectively reduced by the configuration of the sound-absorbing member so as to additionally contribute to noise reduction.

The following advantages are obtained by reducing the sound power of external fans. The homeowners and their neighbors are not disturbed by the loud noise during operation and customer satisfaction is increased.

The sound absorber in no way impairs the functionality of the external fan and merely achieves the desired reduction in sound power.

The member may be used as a component already integrated in the unit when said unit is delivered, or as an accessory to be retrofitted in installations that are already present. 

1. An external fan for an extractor device, the external fan comprising: a fan housing; a ventilator housing arranged in the fan housing, the ventilator housing having an air discharge; and a sound absorbing member arranged in the fan housing and opposite the air discharge of the ventilator housing.
 2. The external fan of claim 1, wherein the sound-absorbing member projects perpendicularly toward the air discharge of the ventilator housing and covers the air discharge completely.
 3. The external fan of claim 1, wherein a thickness of the sound-absorbing member varies across a surface of the sound-absorbing member.
 4. The external fan of claim 3, wherein the sound-absorbing member is thickest at a point that corresponds to a center of the air discharge of the ventilator housing.
 5. The external fan of claim 1, further comprising at least one sound-absorbing lateral part provided in the fan housing, wherein the sound-absorbing lateral part projects perpendicularly toward the air discharge of the ventilator housing outside a surface of the air discharge.
 6. The external fan of claim 1, wherein the fan housing has a housing face, wherein the sound-absorbing member completely covers the housing face of the fan housing, and wherein the housing face is arranged opposite the air discharge of the ventilator housing.
 7. The external fan of claim 6, wherein the fan housing has air outlet openings at at least one of the housing face arranged opposite the air discharge of the ventilator housing and adjacent housing faces.
 8. The external fan of claim 1, wherein the sound-absorbing member has a partition wall that extends perpendicularly to an elevation in the sound-absorbing member.
 9. The external fan of claim 8, wherein the sound-absorbing member has two shells.
 10. The external fan of claim 1, wherein the sound-absorbing member is rotationally symmetrical in shape.
 11. The external fan of claim 1, wherein a distance between a highest point of the sound-absorbing member and the air discharge is at most one third of a diameter of the air discharge.
 12. The external fan of claim 11, wherein the distance is at most one quarter of the diameter of the air discharge.
 13. The external fan of claim 1, wherein the fan housing has two parts; wherein one of the two parts of the fan housing receives the sound-absorbing member; and wherein the one of the two parts has at least one air outlet opening in the fan housing.
 14. The external fan of claim 1, wherein the sound-absorbing member is made of foamed material. 